How is it possible for people to sleep with their eyes open?

Unintentionally: Some individuals eyelids drift apart during sleep, giving them the appearance that their eyes are partially open. A condition, bell's palsy, is an often reversible paralysis, that affects the ability to close the eyelid on one side. Injections of Botox for blepharospasm can sometimes result in temporary failure of eyelid closure. All of these generally result in ocular drying. All not intentional.